BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to an indexable type rotary cutting tool and an indexable
insert used therefor.
2. Description of the Related Art
[0002] Conventionally, there have been dominantly used indexable type rotary cutting tools
using indexable inserts each designed in a triangular shape, a rectangular shape,
a rhombus shape or the like. In these tools, the main cutting edge is of a straight
cutting edge type. A feed per one tooth as a general cutting condition is equal to
0.1 to 0.5 mm/tooth for casting-cutting and 0.1 to 0.3 mm/tooth for steel-cutting
although it is varied according to depth and width of cut. However, such examples
begin to appear that the use of an indexable type rotary cutting tool using a button
insert implements the working at a feed which is not less than about two times as
large as a straight cutting edge, thereby resulting in enhancement of the working
efficiency. This indexable type rotary cutting tool uses button positive type inserts
including various sizes of 8 to 20 mmφ. The clamping mechanisms therefor are broadly
classified into two kinds, one kind being designed to fix the insert by pieces of
a wedge and a supporter, and the other being designed to fix the insert by a fastening
screw inserted into a pin hole disposed at the center of the insert.
[0003] Further, the button insert is slightly large in cutting resistance because of its
shape-dependent characteristic, but longer in length of the cutting edge than the
straight cutting edge, and further high in insert strength; thereby providing many
advantages of making it possible to cut a high hardness material, and then lengthening
the lifetime of the insert, etc. As an example using such a button insert is proposed
tools as described in Japanese Laid-open Patent Application (Kokai) Nos. 9-225724
and 10-118901.
[0004] However, in recent high efficiency working (contour line working), such cases begin
to appear that chattering-vibration is caused during a process of cutting the corner
portions and the grooves, thereby finally causing the inserts to be damaged.
SUMMARY OF THE INVENTION
[0005] It is therefore an object of the present invention to suppress the chattering-vibration
during the cutting process of the corner portions and the grooves to thereby realize
a stable and high efficiency working (contour line working).
[0006] In order to attain the above object, according to a first aspect of the present invention,
there is provided an indexable type rotary cutting tool (1) having at least one indexable
insert, characterized in that the indexable insert (3, 6) has a main cutting edge
(7) and an outer peripheral cutting edge (9), the main cutting edge (7) ranges from
3 to 35 degrees in cutting edge angle (κ) and is shaped like an arc or a substantially
arc, and the outer peripheral cutting edge (9) is shaped like a straight, an arc,
or a substantially arc so as to be back-tapered with respect to the center axis of
the tool.
[0007] Further, according to another aspect of the present invention, there is provided
an indexable insert (3) shaped like a substantial rectangle and having a pin hole
and a relief angle, characterized in that the indexable insert (3) is of a two-corner-used
type, and shaped like a point-symmetry with respect to the center of the pin hole,
each of two sides (9) symmetrical with respect to the center of the pin hole, out
of four sides forming the substantial rectangle, is shaped like a straight line, an
arc or a substantially arc. Each of the other sides out of the four sides comprises
an arc portion (7) shaped like an arc or a substantially arc, and a straight portion
(8) continuing from the arc portion (7), a line segment extending from the arc-center
of the arc portion to the connecting point between the arc portion and the straight
portion intersects to the straight portion at an angle (α) of less than 90 degrees.
[0008] Besides, according to another aspect of the present invention, there is provided
an indexable insert (6) shaped like a triangle and having a pin hole and a relief
angle, characterized in that each of three sides forming the substantial triangle
comprise an arc portion (7) shaped like an arc or a substantially arc and a straight
portion (8) continuing from the arc portion (7), a line segment extending from an
arc-center of the arc portion to the connecting point between the arc portion and
the straight portion intersects to the straight portion at an angle (a) of less than
90 degrees.
[0009] According to the invention, the substantial length of the cutting edge during a cutting
process is substantially constant, thereby resulting in a smooth facing and engraving,
which provides a high efficient working. This results in enhancement of the efficiency
of the contour line working.
[0010] In the indexable type rotary cutting tool according to the present invention, a bottom
edge serve as a main cutting edge. The main cutting edge ranges from 3 to 35 degrees
in cutting edge angle, and is rounded in a radius-round shape. This tool carries out
cutting only at a rounded portion in the neighborhood of the tip thereof and hence
is shorter in the length of the cutting edge than the conventional button insert.
This shortens a substantial length of the cutting edge contacting to the material
to be cut in the cutting process for the corner portions and the grooves which are
small in the draft of the mold and large in cutting stock, thereby preventing occurrence
of the chattering-vibration and thus implementing a stable use of the tool without
trouble. The smaller the cutting edge angle of the main cutting edge is, the more
smooth the cut face is. If the cutting edge angle is less than 3 degrees, the axial
direction-wise depth of cut is reduced, resulting in degradation of the efficiency
and obstruction to the practical use. On the other hand, if the cutting edge angle
exceeds 35 degrees, the main cutting edge is substantially shortened, resulting in
reduction of the lifetime of the insert. More preferably, the cutting edge angle ranges
from 10 to 30 degrees.
[0011] The main cutting edge preferably ranges from 3 to 7 mm in length. The reason why
is that, e.g. in a case where the material to be cut, equivalent to carbon steel S50C
is cut at a feed per one tooth (fz) of 1 to 1.2 mm/tooth, if the length is less than
3 mm, the insert is likely to be defected and thus the lifetime thereof is shortened,
whereas if the length exceeds 7 mm, the cutting resistance is excessively increased.
Therefore, it is preferable that radius of curvature R is increased and that the length
is set to 3 to 7 mm.
[0012] Generally, it is recommended that the length of the main cutting edge is set to 20
to 60% of the diameter of the inscribed circle in the insert. Moreover, so long as
the main cutting edge are rounded at both ends thereof even if it is shaped like a
straight line, it has substantially the same characteristic. Therefore, if the main
cutting edge is shaped like a straight line and then rounded in proper quantity at
both end thereof, the insert is enabled to be formed at a low cost, although the lifetime
is slightly degraded.
[0013] Moreover, in the indexable insert used for this tool, it is preferable that a line
segment extending from an arc-center of the main cutting edge (arc portion) 7 to the
connecting point between the main cutting edge 7 and an inner peripheral cutting edge
(straight portion) 8 intersects to the inner peripheral cutting edge 8 at an angle
of less than 90 degrees (α in Figs. 2 and 4). This is because the angle exceeding
90 degrees makes it difficult to set the main cutting edge within the range from 3
to 35 degrees in cutting edge angle and arrange the inner peripheral cutting edge
at a suitable angle when the insert is mounted to the holder.
Besides, the insert may be an indexable insert which is of a substantially rectangular
and two-corner-used type, and shaped like a point-symmetry with respect to the center
of the pin hole (See Fig. 2). Further, the insert may be an indexable insert which
is of a substantially triangular and three-corner-used type, and has the straight
portion 8 and the arc portion 7 (See Fig. 4).
[0014] The above and other objects, features, and advantages of the invention will more
apparent from the following detailed description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
Fig. 1 is a partial sectional view of an indexable type rotary cutting tool 1 according
to the present invention;
Fig. 2 is a front view of an indexable insert according to an embodiment which is
mounted to the tip portion of the indexable type rotary cutting tool 1 shown in Fig.
1;
Fig. 3 is a side view of the indexable insert;
Fig. 4 is a front view of an indexable insert according to another embodiment of the
invention;
Fig. 5 is a front view of a cutter using an indexable insert of a conventional example;
Fig. 6 is a view useful in explaining the deference between the indexable insert according
to the embodiment of the present invention and that of the conventional example, both
of which repeat cutting during contour line working;
Fig. 7 is a view useful in explaining a manner of carrying out contour line working
by the embodiment of the invention; and
Fig. 8 is view useful in explaining the cutting results of the embodiment of the invention
and the conventional example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Preferred embodiments according to the present invention will be described hereunder
with reference to the accompanying drawings.
[0017] Fig. 1 shows a tool main body 1 to which an insert 3 according to the present invention
is mounted, and Fig. 2 shows a substantially rectangular insert 3 which is an embodiment
of an indexable insert according to the present invention. Fig. 3 is a side view of
the insert 3 shown in Fig. 2.
[0018] As shown in Fig. 1, the rectangular insert 3 shown in Fig. 2 according to the first
embodiment of the invention is fixed to a distal end portion 2 of the tool main body
1 shown in Fig. 1 by inserting a set screw 4 through a pin hole of the insert. Alternatively,
clamping of the insert 3 with a wedge may provide the same performance as is the case
of the fixing of the insert 3 with the set screw 4.
[0019] As shown in Fig. 1, the insert 3 of the first embodiment has a main cutting edge
7 and an outer peripheral cutting edge 9. The main cutting edge 7 is designed in an
arcuate or substantially arcuate shape so that the cutting edge angle (κ) thereof
is within the range from 3 to 35 degrees. The outer peripheral cutting edge 9 is designed
in a straight, arcuate or substantially arcuate shape so as to be back-tapered with
respect to the center axis of the tool.
[0020] The indexable insert 3 of this embodiment is also designed like a point-symmetry
with respect to the center of the pin hole thereof so as to use two corners thereof.
Each of two sides 9 which are symmetrical with respect to the center of the pin hole
in the four sides forming the substantial rectangle is shaped like a straight line,
an arc or a substantial arc. Each of the other sides comprises an arc potion (main
cutting edge) 7 shaped like an arc or a substantially arc, and a straight portion
8 continuing from the arc portion. As shown in Fig. 2, a line segment extending from
the center of the arc of the arc portion 7 to the connecting point between the arc
portion 7 and the straight portion 8 intersects to the straight portion 8 at an angle
(α) which is less than 90 degrees.
[0021] The length of the main cutting edge 7 is preferably set to 3 to 7 mm, however, the
present invention is not limited to this value. Further, when the main cutting edge
7 is shaped like a straight line, it is rounded in proper quantity at both ends thereof.
[0022] Further, Fig. 4 shows a substantially triangular insert 6 according to second embodiment
of the present invention.
[0023] Each of the three sides forming the substantial triangle comprises an arc portion
7 shaped like an arc or a substantially arc, and a straight potion 8 continuing from
the arc potion 8. In this embodiment, a line segment extending from the arc-center
of the arc portion to the connecting point between the arc portion and the straight
portion intersects to the straight portion at an angle (α) which is less than 90 degrees.
[0024] The above structure of the insert 6 of the second embodiment provides a three-corner-used
and indexable insert.
[0025] Fig. 5 shows a radius cutter using a conventional button insert. Fig. 6 is a view
useful in explaining the difference between the conventional button insert and the
rectangular insert of the first embodiment of the invention.
[0026] Next, the comparison test was carried out under the condition that contour lines
were engraved as indicated by arrows in Fig. 7. A tool of 80 mmφ was attached to a
cutter arbor while the overhang length L over a gauge line was set to 270 mm so as
to make it easy to induce the chattering-vibration. Further, the material was worked
in the order of shoulder-cutting, groove-cutting, shoulder-cutting, ... so as to set
the working condition so that the insert was easily defected in the cutting process
of the groove. Further test conditions were given as follows: the material to be cut
was made of S50C as is the case of a cutting test 1, the cutting speed V was set to
200 m/min (number of revolution N = 800 rpm), depth of cut Ad was set to 1.5 mm, width
of cut Rd was set to 40 (shoulder-cutting) to 80 (groove-cutting), and the cutting
style was set to a dry cutting style. The feed per one tooth (fz) was increased while
observing the cut condition. That is, the feed per one tooth (fz) was increased in
turn in the order of 0.25, 0.5, 0.75, 1.0 mm/tooth, while the cut condition was evaluated
from the viewpoint of vibration. Moreover, these fz values will come to 1000, 2000,
3000, 4000 mm/min in terms of the table feed amount F.
[0027] The test results are shown in Fig. 8, in which a mark ⓞ shows "good", a mark Δ shows
"passable", a mark × shows "cutting-impossible". Fig. 8 shows that in the conventional
example, the working is available at the first stage of the contour lines without
problems, the chattering-vibration is increased at the second stage and the subsequent
stages (the depth of cut Ad is not less than 3 mm (depth of cut per one stage 1.5
mm x 2 times) and the working is not available when the feed per one tooth is equal
to 0.75 mm. The third stage had the same result as the second stage. On the other
hand, in the embodiments of the present invention, the material was subjected to satisfactory
working over all the region in which the feed per one tooth fz is 0.25 to 1.00 mm
at the first stage, and also to satisfactory engraving-working through the second,
the third, and the fourth stage also, without the chattering-vibration.
[0028] The reason why such a satisfactory result is obtained will be described with reference
to the schematic view of Fig. 6.
[0029] With respect to the conventional button insert 5, as the depth of cut (Ad) is increased
by 1.5 mm at one time, the length of the cutting edge contacting to the material to
be cut is increased. In other words, in the conventional example, as the depth of
cut Ad is increased like Ad x n-times (cutting number of times) during the contour
line working, the length of the main cutting edge contacting to the material is increased.
[0030] On the contrary, in the embodiments of the invention, the length of the main cutting
edge 7 is set to a value nearly equal to the depth of cut Ad for one time, which enables
the main cutting edge to cut the material without changing its length at the second
stage and the subsequent stages also. In other words, in the embodiment of the invention,
attention is paid to the length of the main cutting edge which is set such that the
chattering-vibration is not caused at the first stage, and this length of the main
cutting edge is set. Therefore, even when the engraving working is carried out at
any frequency, no chattering-vibration occurs, and thus a stable working can be performed.
[0031] Expressing numerically in concrete terms, so long as the machine horse power is allowed
even if the cutter is not so big, when cutting the material of S50C on the condition
that five teeth of 80 mmφ are provided , the cutting speed V is 180 m/min (number
of revolution N is equal to 720 rpm), the depth of cut Ad is set to 1.5 mm, the width
of cut Rd is for groove-cutting, and the feed of one tooth fz is set to 1 mm/tooth,
there could be provided a tool which has the capacities, such as the table feed amount
F of 3600 mm/min and the maximum metal removal rate of 432 cc/min, and on the condition
that the feed per one tooth is 2 mm/tooth, there could be provided a tool which has
the capacities, such as the table feed amount F is 7200 mm/min and the maximum metal
removal rate of 864 cc/min. Taking into consideration that such a cutting process
that the metal removal rate exceeds 200 cc/min is conventionally called "heavy cutting
(high efficient working)", the metal removal rate in the embodiments of the invention
can exceeds two times of 200 cc/min, which shows the superiority of the embodiments
of the invention to the conventional example.
[0032] According to the invention, the substantial length of the cutting edge during a cutting
process is substantially constant, thereby resulting in a smooth facing and engraving,
which provides a high efficient working. This results in enhancement of the efficiency
of the contour line working.
1. An indexable type rotary cutting tool (1) having at least one indexable insert (3,
6), characterized in that
said indexable insert (3, 6) has a main cutting edge (7) and an outer peripheral
cutting edge (9), said main cutting edge (7) ranging from 3 to 35 degrees in cutting
edge angle (K) and being shaped like an arc or a substantially arc, and said outer
peripheral cutting edge (9) is shaped like a straight line, an arc, or a substantially
arc so as to be back-tapered with respect to the center axis of said tool.
2. The indexable type rotary cutting tool as claimed in claim 1, characterized in that
said main cutting edge (7) ranges from 3 to 7 mm in length.
3. The indexable type rotary cutting tool as claimed in any one of claims 1 and 2, characterized
in that said main cutting edge (7) is shaped like a straight line, and is rounded
in proper quantity at both ends thereof
4. An indexable insert (3) shaped like a substantial rectangle and having a pin hole
and a relief angle, characterized in that
said indexable insert (3) is of a two-corner-used type and shaped like a point-symmetry
with respect to a center of said pin hole, each of two sides (9) symmetrical with
respect to said center of said pin hole, out of four sides forming said substantial
rectangle, is shaped like a straight line, an arc or a substantial arc, and each of
the other sides out of said four sides comprises an arc portion (7) shaped like an
arc or a substantially arc, and a straight portion (8) continuing from said arc portion
(7), a line segment extending from an arc-center of said arc portion to the connecting
point between said arc portion and said straight portion intersecting to said straight
portion at an angle (α) of less than 90 degrees.
5. An indexable insert (6) shaped like a triangle and having a pin hole and a relief
angle, characterized in that
three sides forming said substantial triangle comprise an arc portion (7) shaped
like an arc or a substantially arc, and a straight portion (8) continuing from said
arc portion (7), a line segment extending from an arc-center of said arc portion to
the connecting point between said arc portion and said straight portion intersects
to said straight portion at an angle (α) of less than 90 degrees.